Abstract: We present the case of a 91-year-old woman who developed septic arthritis of her knee after undergoing a dental extraction without antibiotic prophylaxis. Arthrocentesis of the left knee resulted in the drainage of purulent fluid and a few calcium pyrophosphate crystals. Synovial culture revealed Prevotella oralis. The relationship between septic arthritis and crystalloid arthropathy is not entirely certain, and in our case, it becomes difficult to assess which was present initially. Crystal arthritis may be a predisposition to a joint space infection, and in recent studies, an unprecedented high rate of gouty arthritis has been reported among a series of patients with septic arthritis of the ankle. This case report underscores the importance of routine synovial fluid analysis and culture in diagnosing joint pathology and supports a role for antibiotic prophylaxis in patients with possible nidi of infection, that is, crystal arthropathies, undergoing invasive procedures.